A data transfer amount of a wireless network has been rapidly increased in recent years. It is because various devices, e.g., a smart phone, a tablet personal computer (PC), or the like, that require machine-to-machine (M2M) communication and a high data transfer amount have been introduced and distributed. To satisfy the required high data transfer amount, a carrier aggregation (CA) technique, a cognitive radio (CR) technique, or the like for effectively using more frequency bands and a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency have recently drawn attention.
In addition, the wireless network has been evolved in a direction of increasing density of nodes capable of accessing to an area around a user. Herein, the node implies an antenna (or antenna group) which is separated from a distributed antenna system (DAS) by more than a certain distance. However, the node is not limited to this definition, and thus can also be used in a broader sense. That is, the node may be a pico-cell eNB (PeNB), a home eNB (HeNB), a remote radio head (RRH), a remote radio unit (RRU), a relay, a distributed antenna (group), etc. A wireless communication system having nodes with higher density can provide higher system performance through cooperation between the nodes. That is, better system performance can be achieved when one base station controller manages transmission and reception of respective nodes and thus the nodes operate as if they are antennas or an antenna group for one cell, in comparison with a case where the respective nodes operate as an independent base station (BS), advanced BS (ABS), Node-B (NB), eNode-B (eNB), access point (AP), etc., and thus do not cooperate with each other. Hereinafter, a wireless communication system including a plurality of nodes is referred to as a multi-node system.
Such a multi-node system has a greater number of transmit (Tx) antennas in comparison with the conventional wireless communication system, and can have various Tx antenna configurations in each node. Therefore, when transmitting a signal according to the conventional multi-input multi-output (MIMO) precoding scheme, the number of MIMO precoding matrices which must be predetermined may be excessively increased. In addition, when transmitting a stream with a different rank in each node, there is a limitation in a MIMO precoding matrix.
Accordingly, there is a need for a signal transmission method for MIMO transmission in a multi-node system.